1. Field of the Invention
The present invention generally relates to a fingerprint sensor module, and more particularly to an optical fingerprint sensor module.
2. The Related Art
Currently, optical fingerprint sensor modules and capacitive fingerprint sensor modules are mainstream products of fingerprint sensor modules on the market. In general, the high-density capacitive fingerprint sensor module is integrated into a chip. When a fingerprint is pressed downward on a surface of the chip, the capacitive fingerprint sensor module senses a fingerprint image through different quantities of electric charge of fingerprint peaks and troughs. The advantage of the capacitive fingerprint sensor module is thinness. But the capacitive fingerprint sensor module has a higher cost, a lower sensing accuracy and a lower durability.
The optical fingerprint sensor module captures the fingerprint image by the principle of imaging. Comparing with the capacitive fingerprint sensor module, the optical fingerprint sensor module has the advantages of higher identification, lower price and better durability. But the imaging system needs to keep a distance from the lens to the sensor to form the fingerprint image clearly. The imaging light path makes a size of the optical fingerprint sensor module become larger and thicker.
Due to a current electronic product being developed towards the trend of thinness, factories wish to manufacture the optical fingerprint sensor modules of which each has a thinner structure one after another for being appropriate to internal structures of the thinner electronic products.
The current optical fingerprint sensor module shortens the straight distance between the sensor and the lens to reduce the thickness of the optical fingerprint sensor module by an imaging light path refracted by a prism. For example, U.S. Pat. No. 8,405,757 discloses a conventional embodiment where a component pressed by the fingerprint is the prism. Through a refraction characteristic of a light the fingerprint image is formed by a prism. It makes the fingerprint image be formed through a total internal reflection light path by the prism to the lens.
In other conventional technology, in order to satisfy the thinness need, the difference is that some is commenced from a structure of the special lens, or a variety of lenses with complex structures are designed to reduce the thickness of the optical fingerprint sensor module for increasing a possibility of being applied in a cell phone or a tablet computer.
However, a structure of the refraction path of the current optical fingerprint sensor module is complex that makes the cost of the fingerprint sensor module is higher and the thickness of the optical fingerprint sensor module has no way of being less than 6.5 mm. Thus, it's difficult to manufacture the current optical fingerprint sensor module in mass production.
In view of this, it's essential to provide an optical fingerprint sensor module with a simple structure, a lower cost and a thickness of being less than 6.5 mm.